1. Field of the Invention
This invention relates to coated calcium hypochlorite compositions having low reactivity in handling, storage and transportation. More specifically, this invention relates to a calcium hypochlorite composition coated with one or more hydrated or anhydrous salts. This invention also relates to a calcium hypochlorite composition additionally coated with at least one active water treatment ingredient as a clarifier, scale inhibitor, dispersant, water softener, corrosion inhibitor, algaecide, fungicide, flocculant, binder or mixtures thereof.
2. Brief Description of Art
Hydrated calcium hypochlorite is classified as a Division-5.1 oxidizer as “dangerous goods” for purposes of transport and storage. As a strong oxidizer, hydrated calcium hypochlorite causes a severe increase in burning intensity and burning rate of combustible materials. Thus, the fire of combustible materials in the presence of hydrated calcium hypochlorite can be quite vigorous. Many efforts have been made to produce hydrated calcium hypochlorite containing products that are not classified as a “Division-5.1 oxidizer” as measured by an internationally recognized standard, i.e. the United Nations Protocol: Transport of Dangerous Good: Manual of Tests and Criteria, Section 34; Classification Procedures, Test Methods, and Criteria relating to Oxidizing Substances of Division 5.1.
Another system for classifying oxidizers is given by the National Fire Protection Association (NFPA). In NFPA 430, Code for the Storage of Liquid and Solid Oxidizer (2004 Edition), the definition of an oxidizer is given as any material that readily yields oxygen or other oxidizing gas, or that readily reacts to promote or initiate combustion of combustible materials and can undergo a vigorous self-sustained decomposition due to contamination or heat exposure. Oxidizers are further broken down according to the degree to which they increase the burning rate of combustible materials as follows:
Class 1: An oxidizer that does not moderately increase the burning rate of combustible materials with which it comes into contact.
Class 2: An oxidizer that causes a moderate increase in the burning rate of combustible materials with which it comes into contact.
Class 3: An oxidizer that causes a severe increase in the burning rate of combustible materials with which it comes into contact.
Class 4: An oxidizer that can undergo an explosive reaction due to contamination or exposure to thermal or physical shock and that causes a severe increase in the burning rate of combustible materials with which it comes into contact.
Calcium hypochlorite is a Class 3 oxidizer according to the NFPA oxidizer classification system.
Recently, U.S. Pat. No. 6,638,446 describes a non Division-5.1 calcium hypochlorite composition consisting of a blend of hydrated calcium hypochlorite and magnesium sulfate heptahydrate. In this invention, the blend comprising of 70 part of 68% calcium hypochlorite and 30 part of magnesium sulfate heptahydrate by total weight of the blend, in which the blend contains at least 17% of total water, and 47% available chlorine, is commercially classified as a non Division-5.1 Oxidizer. Similarly, EP 1464617 A2 discloses a non-Division 5.1 oxidizer tablet having the similar composition of hydrated calcium hypochlorite and magnesium sulfate heptahydrate as described in U.S. Pat. No. 6,638,446. Although these patents discuss the reduced reactivity of the blends, neither U.S. Pat. No. 6,638,446 nor EP 1464617 A2 describes a coated calcium hypochlorite composition.
The approach to coat or encapsulate active hydrated calcium hypochlorite with an inert water-soluble material is well known for the purpose of preventing the contact of calcium hypochlorite and a flammable material and thus to reduce its reactivity and flammability. Several patents have described the processes and coated or encapsulated compositions of hydrated calcium hypochlorite with a variety of coating materials for low reactivity. However, the chemical and physical characterizations of these compositions such as shelf-stability, reactivity, flammability, and Division-5.1 oxidizer classification are not well acknowledged.
For example, the composition disclosed in U.S. Pat. No. 3,953,354 describes an encapsulated calcium hypochlorite composition comprising a core hydrated calcium hypochlorite encapsulated with a coating material consisting with about 5 to about 60% of mixture of calcium hypochlorite dihydrate and about 0.1 to about 15% of a water soluble inert inorganic salt such as NaCl and CaCl2 by weight of the granule. The encapsulated granular product was claimed to resist dusting and caking, and improve retention of its available chlorine on storage. The storage test conducted at 100° C. for 2 hours was not indicative of true storage stability due to the extremely high temperature and very short time frame. The potential for self sustaining decomposition was tested by ignition with lighted matches and burning cigarettes, however, no testing was conducted to determine if the samples would increase the burning rate of combustible materials.
U.S. Pat. Nos. 4,146,676 and 4,048,351 disclose an encapsulation or coating process comprising granular hydrated calcium hypochlorite coated with about 4-46% of a low melting inorganic salt such as aluminum sulfate hydrate by total weight of the encapsulated calcium hypochlorite. Data are given regarding the storage stability, and several of the examples were evaluated for their sensitivity to decomposition by exposure to localized heating (i.e. lighted cigarette) or chemical contamination (i.e. glycerine), however, no testing was conducted to determine if the samples would increase the burning rate of combustible materials. None of the coated compositions was tested according to the Division-5.1 flame test protocol, or evaluated to see if they would increase the burning rate of combustibles.
The compositions disclosed in U.S. Pat. Nos. 4,201,756 and 4,174,411 describe coated calcium hypochlorite with a plurality of layers of inorganic salts which is comprised of chloride, chlorate, nitrate, bromide, bromate, or sulfate salts of Periodic Table Group I alkali metal salts (sodium, potassium, lithium, rubidium, cesium or francium). The layers of salts form a physical barrier, which was claimed to resist dusting and degradation during handling, and also decreases propensity for ignition and self-sustained decomposition when contacted by a lighted match or incompatible organic materials. However, there is little data to support these claims and no data to show whether any of these compositions is a non Division-5.1 oxidizer or if they increase the burning rate of combustibles.
U.S. Pat. No. 4,276,349 described a process for encapsulating calcium hypochlorite that is comprised of a core of calcium hypochlorite encapsulated with a plurality of rounded layers containing a mixture of high percentage of water soluble inorganic salts and calcium hypochlorite. None of the compositions made from the process in the art were specifically characterized and tested for their storage stability and flammability, particularly, according to Division-5.1 Oxidizer classification.
In addition, US Patent Application No. 2003/0038277 A1 and PCT Application WO 03/014013 A2 recently describes a blended or coated calcium hypochlorite process and composition consisting of a polymeric alkali salt and calcium hypochlorite. The composition disclosed in the patent describes an improved environmental stability such as anti-flammability by a brake fluid oil test. However, the actual compositions tested in the arts including contents of available chlorine and moisture were not known and specified, and none of the compositions was tested according to the Division-5.1 flame test protocol, and there is little data to support these claims.
The idea to coat or encapsulate active calcium hypochlorite with an inert water soluble inorganic salt in these prior art references was to reduce the contact of calcium hypochlorite and a flammable material and thus to reduce its reactivity and flammability. The particles with a coating of an inorganic salt as the exterior layer have an increased degree of resistance to ignition by lighted cigarettes or the reaction caused when contacted with organic materials. However, ignition tests are quite different in principle from the above oxidizer classification test and the NFPA classification system which rate the increase in burning rate of combustible materials after ignition has already been initiated. The former is a prevention test of ignition of the material when contact with a lighted match, while the UN oxidizer classification test is to determine the potential to increase the burning rate or the burning intensity of the combustible cellulose when two are thoroughly mixed in a specific ratio, by mass, with the product to cellulose. Since little or no fuel is present in the ignition tests, the procedure does not test the oxidizing properties or the ability to increase the burning rate of combustible materials. Many substances will pass the ignition tests, but will still be classified as Division 5.1 Oxidizers.
One of the examples as described in U.S. Pat. No. 4,201,756 was that calcium hypochlorite encapsulated with about 21% of sodium chloride by total weight of the composition prevented ignition of the material when contacted with a lighted match, but it failed to undergo self-sustained decomposition. In contrast, the blend of calcium hypochlorite and sodium chloride by the same weight composition actually accelerate burning, as indicated in U.S. Pat. No. 6,638,446.
Therefore, it is difficult to predict whether any compositions in the prior art can be classified as a non Division-5.1 Oxidizer or as NFPA Class 1 or Class 2 oxidizers. Indeed, a coated non Division-5.1, NFPA Class 1 or NFPA Class 2 granular calcium hypochlorite is not seen both in either the marketplace or the literature.
Accordingly, there is an increasing need in this art to produce a calcium hypochlorite product having high available chlorine that is not classified as a Division 5.1 Oxidizer or NFPA Class 3 oxidizer and which has enhanced safety (i.e. diminished fire producing) properties. Therefore, this invention, by providing a solution to that need, is to specifically describe coated calcium hypochlorite compositions with high available chlorine that is not a Division-5.1 oxidizer or NFPA Class 3 oxidizer, that shows excellent storage stability, and has additional advantages for water treatments. These coated calcium hypochlorite compositions are not considered as dangerous goods for transportation and storage, and thus will provide greater public safety.
In addition, the coated calcium hypochlorite composition of the present invention may provide a composition, which is not a non Division-5.1 oxidizer or NFPA Class 3 oxidizer, but with higher available chlorine, lower reactivity and multifunctional benefits than their corresponding blends for water treatments and cleaning applications.